Fan control apparatus and fan control method

ABSTRACT

A fan controlling apparatus for controlling a plurality of fans which are tandemly arranged in ventilation direction of a chamber to control a temperature of a hot generating object placed in the chamber, the apparatus includes a memory for storing data of the rotational speed each of fans in relation to the temperature of the heat generating object, and a controller for controlling the rotational speed of each of the fans respectively in dependence on the temperature of the heat generating object in reference to the data stored in the memory.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of theprior Japanese Patent Application No. 2009-123500, filed on May 21,2009, the entire contents of which are incorporated herein by reference.

FIELD

The embodiments discussed herein are relates to a fan control apparatusand a fan control method.

BACKGROUND

In existing electronic equipment such as a server device, a PC (PersonalComputer) and others, in some cases, fans that send air into equipmentconcerned to radiate heat in the equipment to the outside in order toavoid temperature rising in the equipment with heat generated from aprocessor or the like are mounted on the equipment.

In a fan, noise (whirring sounds) is generated owing to formation of aireddies in the vicinity of blades. Noise generated from a fan isincreased with increasing an air flow rate at which the fan blows offair. Therefore, if it is intended to increase the number of revolutions(hereinafter, referred to as the revolution number) of the fan toincrease the air flow rate, the noise will be increased accordingly.Specifically, it is known that noise from a fan is proportional to thefifth or sixth power of the number of axial rotations of the fan.

Recently, such a situation has been more and more frequently observedthat electronic equipment is installed not only in a specific place suchas a computer room but also in a general office and hence consciousnessof noise reduction is now being raised. Therefore, how the noisegenerated from a fan is reduced is one of important problems to besolved.

As a method of reducing noise generated from a fan, a method ofmonitoring the temperature of a heating element and the environmentaltemperature around the heating element and changing the revolutionnumber of the fan concerned in accordance with the temperatures somonitored to control the noise from the fan so as not to increase morethan needed is known. The revolution number of the fan is controlled bymodulating the pulse width (the PWM value) of a voltage or PWM (PulseWidth Modulation) signal to control energy to be supplied to the motorof the fan.

On the hand, nowadays, in some cases, a space for an air passage inequipment is reduced with size and thickness reduction of the electronicequipment and such a case in which only a small fan is allowed to beinstalled is now being more frequently observed. In addition, a heatingvalue of electronic equipment is more and more increased every year asprocessing speed and performance of electronic equipment get higher.Thus, such a countermeasure is taken that a plurality of fans issuperposed on one another in a multi-stage form so as to sufficientlycool the inside of electronic equipment even when installation of onlysmall-sized fans is allowed.

In this connection, an example in which a plurality of fans issuperposed on one another in a multi-stage form is illustrated in FIG.26. FIG. 26 illustrates an example of electronic equipment in which twofans are disposed in series.

As illustrated in FIG. 26, two fans 321 a and 321 b are installed inseries in an air passage 310 of electronic equipment 300. The electronicequipment 300 includes a fan power source section 330 and a controlsection 340. The fan power source section 330 is a power source forsupplying power to motors not illustrated which are built in the fans321 a and 321 b. The control section 340 controls amounts of energysupplied to the fans 321 a and 321 b on the basis of temperatures ofheating elements 350 a and 350 b detected using temperature sensors 341a and 341 b and an environmental temperature detected using atemperature sensor 341 c. Next, a specific configuration of the controlsection 340 will be illustrated. FIG. 27 is a block diagram illustratinga configuration of the existing control section 340.

As illustrated in FIG. 27, the control section 340 includes thetemperature sensors 341 a to 341 c, temperature check sections 342 a and342 b, revolution number detecting sections 343 a and 343 b, arevolution number error check section 344 and a pulse generator 345. Thecontrol section 340 also includes a RAM (Random Access Memory) 346, aROM (Read Only Memory) 347 and a processor 348.

The temperature sensors 341 a and 341 b are attached to the heatingelements 350 a and 350 b in the electronic equipment 300 to detect thetemperatures of the heating elements 350 a and 350 b. The temperaturesensor 341 c is installed outside of the electronic equipment 300 todetect the environmental temperature around the fan 321 a. Thetemperature check sections 342 a and 342 b check to see to which extentthe temperatures of the heating elements 350 a and 350 b detected usingthe temperature sensors 341 a and 341 b vary from a target temperatureand notify the processor 348 of results of check in the form ofpredetermined variables.

The revolution number detecting sections 343 a and 343 b detect therevolution numbers of the fans 321 a and 321 b. The revolution numbercheck section 344 checks to see whether the fans 321 a and 321 bnormally rotate on the basis of the revolution numbers of the fans 321 aand 321 b detected using the revolution number detecting sections 343 aand 343 b and notifies the processor 348 of a result of check. The pulsegenerator 345 inputs pulses for controlling the revolution numbers ofthe fans 321 a and 321 b into the fans 321 a and 321 b in pulse widthsin accordance with an instruction from the processor 348.

The ROM 347 stores therein a table indicating predetermined variablescorresponding to temperatures of the heating elements 350 a and 350 band PWM values of pulses to be input into the heating elements 350 a and350 b in one-to-one correspondence and a table indicating environmentaltemperatures and the PWM values in one-to-one correspondence. Theprocessor 348 determines the pulse widths of pulses to be output to thefans 321 a and 321 b on the basis of the predetermined variables sentfrom the temperature check sections 342 a and 342 b and theenvironmental temperature detected using the temperature sensor 341 c. Aspecific example thereof is as illustrated in FIG. 27. FIG. 28 is aflowchart illustrating an example of procedures of processing executedusing the existing processor 348.

As illustrated in FIG. 28, first, the processor 348 performs temperaturemeasurement (step S001). That is, the processor 348 acquirespredetermined variables corresponding to the temperatures of the heatingelements 350 a and 350 b detected using the temperature sensors 341 aand 341 b from the temperature check sections 342 a and 342 b. Theprocessor 348 also acquires the environmental temperature detected usingthe temperature sensor 341 c.

Next, the processor 348 instructs the pulse generator 345 to modulatethe pulse widths on the basis of results of measurement of theenvironmental temperature and the temperatures of the heating elements350 a and 350 b (step S002). Specifically, first, the processor 348determines PWM values corresponding to the predetermined variablesacquired from the temperature check sections 342 a and 342 b or theenvironmental temperature acquired from the temperature sensor 341 c onthe basis of the tables stored in the ROM 347. Then, the processor 348instructs the pulse generator 345 to modulate widths of pulses to beinput into the fans 321 a and 321 b to have the PWM values so determined(step S002).

The pulse generator 345 then inputs pulses whose widths have beenmodulated to have the PWM values as instructed from the processor 348.As a result, the revolution numbers of the fans 321 a and 321 b arechanged to the revolution numbers conforming to the environmentaltemperature and the temperatures of the heating elements 350 a and 350b. As described above, the existing processor 348 determines the pulsewidths on the basis of the environmental temperature and thetemperatures of the heating elements 350 a and 350 b. Incidentally, theexisting control section 340 detects the revolution numbers of the fans321 a and 321 b using the revolution number detecting sections 343 a and343 b to check on errors in the revolution numbers. Specifically, theprocessor 348 sends an error notification that the fans 321 a and 321 bare now in stopped states to the electronic equipment 300 on the basisof results of revolution number error check acquired from the revolutionnumber error check section 344.

Incidentally, hitherto, the control section 340 has controlled the fans321 a and 321 b in the same manner. In the following, the fan 321 awhich is situated on the side of taking air into the equipment from theoutside will be referred to as a front-stage fan 321 a and the fan 321 bwhich is situated on the side of sending the air into the electronicequipment 300 will be referred to as a rear-stage fan 321 b.

The processor 348 determines a pulse width of a pulse which is commonlyinput into the front-stage fan 321 a and the rear-stage fan 321 b atstep S002 in FIG. 28 and notifies the pulse generator 345 of the pulsewidth. As a result, hitherto, energy of the same amount has been usuallysupplied from the pulse generator 345 to the front-stage fan 321 a andthe rear-stage fan 321 b as illustrated in FIG. 29.

However, in the case that the fans 321 a and 321 b are superposed oneach other in a multi-stage form, the work amount with which therear-stage fan 321 b blows off air is reduced influenced by an aircurrent generated from the front-stage fan 321 a. Therefore, if theamount of energy supplied to the front-stage fan 321 a is the same asthat supplied to the rear-stage fan 321 b, the rear-stage fan 321 b willrun idle and hence the revolution number of the rear-stage fan 321 bwill be increased. Noise is generated greatly influenced by theoperation of the fan of the largest revolution number and hence anincrease in revolution number of the rear-stage fan 321 b will be amajor factor to cause an increase in noise.

In this connection, a technique for, example, making the revolutionnumber of the front-stage fan 321 a different from that of therear-stage fan 321 b is known. Specifically, in the above mentionedtechnique, the pulse width of a pulse input into the rear-stage fan 321b is controlled to become shorter than that of a pulse input into thefront-stage fan 321 a. In the above mentioned case, if the revolutionnumber of the rear-stage fan 321 b is reduced, an air flow rate (neededair flow rate) needed to cool heating elements may not be possiblyobtained. Therefore, it may become needed to increase the revolutionnumber of the front-stage fan 321 a more than that needed when theenergy of the same amount is applied to each of the fans 321 a and 321b. An example of the above mentioned technique is disclosed, forexample, in Japanese Laid-open Patent Publication No. 2004-179186.

However, in the above mentioned known technique, the revolution numberof the front-stage fan 321 a is simply increased with no considerationof the system impedance characteristic of the electronic equipment 300,so that the noise may be rather increased as compared with a case inwhich the energy of the same amount is applied to each of the fans 321 aand 321 b. The system impedance characteristic is a pressure lossdetermined from a density at which components constituting theelectronic equipment 300 are packaged and the shape of an air passagetherein and is a characteristic intrinsic to the electronic equipment300 concerned.

That is, the noise generated from the fans 321 a and 321 b variesdepending on the characteristics and the shapes of these fans 321 a and321 b and also depending on the configuration of the electronicequipment 300 concerned on which the fans 321 a and 321 b are mountedand locations of the fans 321 a and 321 b in the electronic equipment300 concerned. Therefore, if the revolution number of the front-stagefan 321 a is simply increased, the noise generated from the front-stagefan 321 a may be possibly increased more than the noise generated fromthe rear-stage fan 321 b when the energy of the same amount is appliedto each of the fans 321 a and 321 b depending on the locations of thefans.

SUMMARY

According to an aspect of the embodiments, a fan controlling apparatusfor controlling a plurality of fans which are tandemly arranged inventilation direction of a chamber to control a temperature of a hotgenerating object placed in the chamber, the apparatus includes a memoryfor storing data of the rotational speed each of fans in relation to thetemperature of the heat generating object, and, a controller forcontrolling the rotational speed of each of the fans respectively independence on the temperature of the heat generating object in referenceto the data stored in the memory.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe claims. It is to be understood that both the foregoing generaldescription and the following detailed description are exemplary andexplanatory and are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating a configuration of a fan controldevice according to an embodiment 1;

FIG. 2 is a diagram illustrating a configuration of electronic equipmentaccording to an embodiment 2;

FIG. 3 is a block diagram illustrating a configuration of a fan controldevice according to the embodiment 2;

FIG. 4 is a block diagram illustrating specific configurations of aprocessor and a ROM according to the embodiment 2;

FIG. 5 is a diagram illustrating an example of an equipment statemanagement table;

FIG. 6 is a diagram illustrating information stored in a control datastorage section according to the embodiment 2;

FIG. 7A is a diagram illustrating an example of aheating-element-temperature-based PWM value determination table;

FIG. 7B is a diagram illustrating an example of anenvironmental-temperature-based PWM value determination table;

FIG. 8 is a diagram explaining a difference between energy supplied to afront-stage fan and energy supplied to a rear-stage fan;

FIG. 9 is a diagram illustrating a specific configuration of a databasepreparing section according to the embodiment 2;

FIG. 10 is a flowchart illustrating an example of procedures ofpreparing the heating-element-temperature-based PWM value determinationtable and the environmental-temperature-based PWM value determinationtable;

FIG. 11 is a flowchart illustrating an example of procedures ofprocessing executed using the processor according to the embodiment 2;

FIG. 12 is a diagram illustrating effects brought about by theembodiment 2;

FIG. 13 is a diagram illustrating examples of measurement conditionsinvolving experiments for validation;

FIG. 14A is a diagram illustrating data indicative of a result ofmeasurement of the front-stage revolution number, the rear-stagerevolution number and the device noise performed under a measurementcondition A;

FIG. 14B is a diagram illustrating data indicative of a result ofmeasurement of the front-stage revolution number, the rear-stagerevolution number and the consumption power performed under themeasurement condition A;

FIG. 14C is a diagram illustrating data indicative of a result ofanalysis of frequencies of the device noise performed under themeasurement condition A;

FIG. 15A is a diagram illustrating a result of measurement performedunder a condition A-1;

FIG. 15B is a diagram illustrating a result of measurement performedunder a condition A-2;

FIG. 15C is a diagram illustrating a result of measurement performedunder a condition A-3;

FIG. 16A is a diagram illustrating data indicative of a result ofmeasurement of the front-stage average revolution number, the rear-stageaverage revolution number and the device noise performed underconditions B-1 and B-2;

FIG. 16B is a diagram illustrating data indicative of a result ofmeasurement of the front-stage average revolution number, the rear-stageaverage revolution number and the consumption power performed under theconditions B-1 and B-2;

FIG. 16C is a diagram illustrating data indicative of a result ofanalysis of frequencies of the device noise performed under theconditions B1 and B2;

FIG. 17A is a diagram illustrating a result of measurement performedunder the condition B-1;

FIG. 17B is a diagram illustrating a result of measurement performedunder the condition B-2;

FIG. 18A is a diagram illustrating data indicative of a result ofmeasurement of the front-stage average revolution number, the rear-stageaverage revolution number and the device noise performed underconditions B-3 and B-4;

FIG. 18B is a diagram illustrating data indicative of a result ofmeasurement of the front-stage average revolution number, the rear-stageaverage revolution number and the consumption power performed under theconditions B-3 and B-4;

FIG. 18C is a diagram illustrating data indicative of a result ofanalysis of frequencies of the device noise performed under theconditions B3 and B4;

FIG. 19A is a diagram illustrating a result of measurement performedunder the condition B-3;

FIG. 19B is a diagram illustrating a result of measurement performedunder the condition B-4;

FIG. 20 is a functional block diagram illustrating an example of acomputer for executing a fan control program;

FIG. 21 is a block diagram illustrating a configuration of a fan controldevice according to an embodiment 3;

FIG. 22 is a block diagram illustrating specific configurations of aprocessor and a ROM according to the embodiment 3;

FIG. 23 is a diagram illustrating information stored in a control datastorage section according to the embodiment 3;

FIG. 24 is a diagram illustrating an example of a rear-stage PWN valuechange table;

FIG. 25 is a flowchart illustrating an example of procedures ofprocessing executed using the processor according to the embodiment 3;

FIG. 26 is a diagram illustrating an example of electronic equipment inwhich two fans are disposed in series;

FIG. 27 is a block diagram illustrating a configuration of an existingcontrol section;

FIG. 28 is a flowchart illustrating an example of procedures ofprocessing executed using an existing processor; and

FIG. 29 is a diagram illustrating that the amount of energy supplied toa front-stage fan is the same as that supplied to a rear-stage fan.

DESCRIPTION OF EMBODIMENTS

Next, preferred embodiments of a fan control device, a fan controlmethod and a fan control program disclosed in the present applicationwill be described in detail with reference to the accompanying drawings.

Embodiment 1

A fan control device according to an embodiment 1 will be described. Thefan control device according to the embodiment 1 is a control devicethat controls operational conditions of a plurality of fans disposed inseries relative to an air passage formed in equipment.

The plurality of fans blow off air to heating elements disposed in theequipment to forcibly air-cool the heating elements. The fan controldevice controls the revolution number of each of the plurality of fans.FIG. 1 is a block diagram illustrating a configuration of the fancontrol device according to the embodiment 1.

As illustrated in FIG. 1, a fan control device 500 according to theembodiment 1 includes a temperature detecting section 510 and a controlsection 520. The temperature detecting section 510 detects thetemperature of each heating element. The control section 520 thencontrols the revolution numbers of the fans such that an air flow rateneeded for cooling the heating elements is obtained in a state that therevolution numbers of the fans coincide with each other on the basis ofthe temperatures of the heating elements detected using the temperaturedetecting section 510.

Specifically, the control section 520 according to the embodiment 1controls the revolution numbers of the fans such that the needed airflow rate (the cooling air flow rate) needed to cool the heatingelements obtained from the temperatures of the heating elements, thepipeline resistance in the equipment and the total static pressure-airflow rate characteristic of the fans in a state in which a difference inrevolution number between the fans is in a predetermined tolerance isacquired and the difference in revolution number between the fans is setin the predetermined tolerance. By controlling the revolution number ofeach fan in the above mentioned manner, the respective fans rotate in astate in which the difference in revolution number between the fans ismaintained in the predetermined tolerance, that is, rotate in a state inwhich the revolution numbers of the respective fans coincide with eachother in the predetermined tolerance to send air to the heating elementsat a needed air flow rate determined in accordance with the currenttemperature of each heating element.

As described above, the fan control device 500 according to theembodiment 1 controls so as to maintain the difference in revolutionnumber between the fans in the predetermined tolerance, desirably, so asto control the revolution numbers of the fans to coincide with eachother. Therefore, such a situation may be avoided that the total noisegenerated from the fans is increased owing to surplus noise generatedfrom a fan of the largest revolution number.

The needed air flow rate attained according to the embodiment 1 isobtained by taking the temperatures of the heating elements, thepipeline resistance in the equipment and the total static pressure-airflow rate characteristic of the fans obtained in a state in which thedifference in revolution number between the fans is maintained in thepredetermined tolerance into consideration. Therefore, according to theembodiment 1, the air flow rate suited to cool the heating elements maybe obtained in a state in which the difference in revolution numberbetween the fans is maintained in the predetermined tolerance regardlessof the configuration of the equipment and the locations of the fans inthe equipment.

Therefore, according to the embodiment 1, it may be possible to reducethe noise generated from the plurality of fans while obtaining the airflow rate needed for cooling the heating elements in the equipment usingthe plurality of fans.

Embodiment 2

Next, a fan control device according to an embodiment 2 will bedescribed. The fan control device according to the embodiment 2 isconfigured to control the revolution numbers of two fans installed inelectronic equipment such as a rack-mounted type server device, ageneral PC and others. First, a configuration of electronic equipment inwhich the fan control device according to the embodiment 2 is installedwill be described. FIG. 2 is a diagram illustrating a configuration ofthe electronic equipment according to the embodiment 2.

As illustrated in FIG. 2, electronic equipment 50 according to theembodiment 2 includes two fans 3 a, 3 b and heating elements 52 a and 52b such as processors installed in an air passage 51 formed in theelectronic equipment 50.

The fans 3 a and 3 b are axial fans of the same shape andcharacteristic. The fans 3 a and 3 b are disposed in series relative tothe air passage 51 and generate air currents flowing from the fan 3 atoward the fan 3 b to forcibly air-cool the heating elements 52 a and 52b disposed downstream of the air currents. In the following, of the fans3 a and 3 b, the fan 3 a for sucking air from the outside of theelectronic equipment 50 will be referred to as a front-stage fan and thefan 3 b for distributing the air which has been sucked using thefront-stage fan 3 a into the electronic equipment 50 will be referred toas a rear-stage fan.

The electronic equipment 50 also includes a fan control device 1 and afan power source section 2 installed outside of the air passage 51. Thefan power source section 2 is a power source for supplying power tomotors not shown which are built in the fans 3 a and 3 b. That is, whenthe power is supplied from the fan power source section 2, the motors ofthe fans 3 a and 3 b rotate and blades attached to the motors rotate incooperation with the rotation of the motors, and hence the fans 3 a and3 b generate air currents flowing toward the heating elements 52 a and52 b.

The fan control device 1 detects the temperatures of the heatingelements 52 a and 52 b and the temperature (the environmentaltemperature) outside of the electronic equipment 50 using temperaturesensors 11 a to 11 c. The fan control device 1 then controls therevolution numbers of the fans 3 a and 3 b so as to obtain an air flowrate needed for cooling the heating elements 52 a and 52 b in a state inwhich the difference in revolution number between the fans 3 a and 3 bis maintained in the predetermined tolerance on the basis of thetemperatures detected using the temperature sensors 11 a to 11 c. Next,a specific configuration of the fan control device 1 described abovewill be illustrated. FIG. 3 is a block diagram illustrating aconfiguration of the fan control device according to the embodiment 2.

As illustrated in FIG. 3, the fan control device 1 includes thetemperature sensors 11 a to 11 c, temperature check sections 12 a and 12b, revolution number detecting sections 13 a and 13 b, a revolutionnumber error check section 14 and pulse generators 15 a and 15 b. Thefan control device 1 also includes a RAM 16, a ROM 17 and a processor18.

The temperature sensors 11 a and 11 b are attached to the heatingelements 52 a and 52 b and detect the temperatures of the heatingelements 52 a and 52 b. The temperature sensor 11C is disposed outsideof the electronic equipment 50 and detects the environmental temperaturearound the front-stage fan 3 a. The temperature sensors 12 a and 12 bcheck to see to which extent the temperatures of the heating elements 52a and 52 b detected using the temperature sensors 11 a and 11 b arevaried from a target temperature and notify the processor 18 of resultsof check in the form of predetermined variables.

The revolution number detecting sections 13 a and 13 b are, for example,pulse counters and respectively detect the revolution numbers of thefans 3 a and 3 b. The revolution number error check section 14 checks tosee whether the fans 3 a and 3 b normally rotate on the basis of therevolution numbers of the fans 3 a and 3 b detected using the revolutionnumber detecting sections 13 a and 13 b and notifies the processor 18 ofa result of check.

The pulse generators 15 a and 15 b input pulses used to control therevolution numbers of the fans 3 a and 3 b in pulse widths (PWM values)as instructed from the processor 18 into the fans 3 a and 3 b.Specifically, the pulse generator 15 a inputs a pulse of a PWM value asinstructed from the processor 18 into the front-stage fan 3 a. The pulsegenerator 15 b inputs a pulse of a PWM value as instructed from theprocessor 18 into the rear-stage fan 3 b. As a result, the fans 3 a and3 b rotate with the revolution numbers conforming to the pulse widths ofthe pulses input from the pulse generators 15 a and 15 b.

The ROM 17 stores therein various pieces of data needed for processingexecuted using the processor 18. The processor 18 determines PWM valuesof pulses to be input into the front-stage fan 3 a and the rear-stagefan 3 b on the basis of the temperatures detected using the temperaturesensors 11 a to 11 c. Next, specific configurations of the processor 18and the ROM 17 according to the embodiment 2 will be described. FIG. 4is a block diagram illustrating the specific configurations of theprocessor 18 and the ROM 17 according to the embodiment 2.

As illustrated in FIG. 4, the ROM 17 includes an equipment state storagesection 171 and a control data storage section 172. The equipment statestorage section 171 stores an equipment state management table. Theequipment state management table is a table used to specify the systemimpedance (the pipeline resistance) corresponding to the currentconfiguration of the electronic equipment 50. FIG. 5 illustrates anexample of the equipment state management table 61.

As illustrated in FIG. 5, in equipment state management table 61, systemimpedances and one equipment state specification flag are stored suchthat the flag corresponds to one of the impedances. In the exampleillustrated in the drawing, the impedance is a pressure loss determinedfrom a density rate at which the respective components of the electronicequipment 50 are packaged and the shape of an air passage in theequipment. In the equipment state management table 61 according to theembodiment 2, a plurality of impedances measured by changing theconfiguration of the electronic equipment 50 are stored and theequipment state specification flag is set for a system impedancecorresponding to the current configuration of the electronic equipment50.

For example, in the equipment state management table 61 illustrated inFIG. 5, system impedances A to C respectively measured by changing theconfiguration of the electronic equipment 50 are stored and theelectronic state specification flag is set for the system impedance A.That is, the equipment state management table 61 illustrated in FIG. 5indicates that the system impedance corresponding to the currentconfiguration of the electronic equipment 50 is “A”. In the case thatthe configuration of the electronic equipment has been changed, theequipment state management table 61 is manually updated by a user of theelectronic equipment 50. Owing to the above mentioned operation, evenwhen the configuration of the electronic equipment 50 has been changed,the system impedance corresponding to a fresh configuration of theelectronic equipment 50 may be specified.

The control data storage section 172 stores aheating-element-temperature-based PWM value determination table and anenvironmental-temperature-based PWM value determination table. Theheating-element-temperature-based PWM value determination table is atable used to specify PWM values of pulses to be input into the fans 3 aand 3 b on the basis of the temperatures of the heating elements 52 aand 52 b. The environmental-temperature-based PWM value determinationtable is a table used to specify PWM values of pulses to be input intothe fans 3 a and 3 b on the basis of the environmental temperature.Next, these pieces of information stored in the control data storagesection 172 will be specifically described. FIG. 6 is a diagram forexplaining information stored in the control data storage section 172according to the embodiment 2.

As illustrated in FIG. 6, the control data storage section 172 storesheating-element-temperature-based PWM value determination tables 71 a to71 c and environmental-temperature-based PWM value determination tables72 a to 72 c in one-to-one correspondence with the plurality of systemimpedances A to C. Specifically, the control data storage section 172stores the heating-element-temperature-based PWM value determinationtable 71 a and the environmental-temperature-based PWM valuedetermination table 72 a corresponding to the system impedance A. Thecontrol data storage section 172 also stores theheating-element-temperature-based PWM value determination table 71 b andthe environmental-temperature-based PWM value determination table 72 bcorresponding to the system impedance B. The control data storagesection 172 further stores the heating-element-temperature-based PWMvalue determination table 71 c and the environmental-temperature-basedPWM value determination table 72 c corresponding to the system impedanceC.

FIG. 7A illustrates an example of the heating-element-temperature-basedPWM value determination table 71 a. As illustrated in FIG. 7A, in theheating-element-temperature-based PWM value determination table 71 a,heating element temperatures, common revolution numbers, front-stage PWMvalues and rear-stage PWM values are stored in one-to-onecorrespondence. For example, as illustrated in FIG. 7A, in theheating-element-temperature-based PWM value determination table 71 a,the common revolution number “aaa”, the front-stage PWM value “Nfa” andthe rear-stage PWM value “Nra” are stored corresponding to the heatingelement temperature “A”. The heating element temperatures are stored inthe form of predetermined variables output from the temperature checksections 12 a and 12 b in accordance with the temperatures of theheating elements 52 a and 52 b.

The common revolution number (min⁻¹) is a revolution number commonly setfor the fans 3 a and 3 b in the case that an air flow rate needed forcooling the heating elements 52 a and 52 b is obtained in a state inwhich a difference in revolution number between the fans 3 a and 3 b ismaintained in a predetermined tolerance. In the example illustrated inFIG. 7A, the needed air flow rate stored in theheating-element-temperature-based PWM value determination tables 71 a to71 c is an air flow rate determined in accordance with temperatures ofthe heating elements 52 a and 52 b, a system impedance in the electronicequipment 50 and a total PQ characteristic (a static pressure-air flowrate characteristic) of the fans 3 a and 3 b obtained in a state inwhich the difference in revolution number between the fans 3 a and 3 bis maintained in the predetermined tolerance. Incidentally, the systemimpedance, the PQ characteristic and the common revolution number areobtained from thermal hydraulic simulation and measurement performed onthe basis of measurement of temperatures of the heating elements 52 aand 52 b. Details thereof will be described later.

In this embodiment, the “predetermined tolerance” is a range in whichthe difference in revolution number between the front-stage fan 3 a andthe rear-stage fan 3 b is less than 10%. That is, ideally, the noisegenerated from these fans 3 a and 3 b may be minimized by controllingthe revolution number of the front-stage fan 3 a to coincide with thatof the rear-stage fan 3 b. However, even in the case that the revolutionnumber of the front-stage fan 3 a is slightly different from that of therear-stage fan 3 b, any problem will not cause as long as an error innoise caused by the slight difference of the revolution number of thefront-stage fan from that of the rear-stag fan is so small that it isnot recognized with human's ears. In the case that the difference inrevolution number between the front-stage fan 3 a and the rear-stage fan3 b is 10%, the noise generated from these fans 3 a and 3 b is largerthan the noise generated when the revolution numbers of the front-stageblower 3 a and the rear-stage blower 3 b are controlled to coincide witheach other by about 3 dB. Basically, it is said that the error of 3 dBis not recognized with human's ears. Therefore, in this embodiment, the“predetermined tolerance” is defined as a range in which the differencein revolution number between the front-stage fan 3 a and the rear-stagefan 3 b is less than 10%.

However, some persons may recognize the error of 3 dB with their ears,so that, more preferably, the difference in revolution number betweenthe front-stage blower 3 a and the rear-stage blower 3 b is set to beless than 5%. With the difference in revolution number between thefront-stage fan 3 a and the rear-stage fan 3 b of less than 5%, thenoise generated from the front-stage fan 3 a and the rear-stage fan 3 bbecomes larger than the noise generated when the revolution numbers ofthe front-stage fan 3 a and the rear-stage fan 3 b are controlled tocoincide with each other by about 1 dB. As described above, a noisereduction effect which is equivalent to that attained when therevolution numbers of the front-stage fan 3 a and the rear-stage fan 3 bare controlled to coincide with each other may be more obtained bysetting the “predetermined tolerance” to a range in which the differencein revolution number between the front-stage fan 3 a and the rear-stagefan 3 b is less than 5%.

The front-stage PWM value (s) is a PWM value of a pulse to be input intothe front-stage fan 3 a in order to rotate the front-stage fan 3 a witha common revolution number. The rear-stage PWM value (s) is a PWM valueof a pulse to be input into the rear-stage fan 3 b in order to rotatethe rear-stage fan 3 b with the common revolution number. That is, forexample, when the heating element temperature is “A”, the pulse of thefront-stage PWM value “Nfa” is input into the front-stage fan 3 a andthe pulse of the rear-stage PWM value “Nra” corresponding to thefront-stage PWM value “Nfa” is input into the rear-stage fan 3 b,thereby rotating the fans 3 a and 3 b with the common revolution number“aaa”. These front-stage and rear-stage PWM values may be obtained frommeasurement performed in advance.

FIG. 7B illustrates an example of the environmental-temperature-basedPWM value determination table 72 a. As illustrated in FIG. 7B,environmental temperatures, common revolution numbers, front-stage PWMvalues and rear-stage PWM values are stored in theenvironmental-temperature-based PWM value determination table 72 a inone-to-one correspondence. For example, as illustrated in FIG. 7B, thecommon revolution number “fff”, the front-stage PWM value “Nff” and therear-stage PWM value “Nrf” are stored in theenvironmental-temperature-based PWM value determination table 72 acorresponding to the heating element temperature “F”. In the exampleillustrated in the drawing, the environmental temperature is atemperature detected using the temperature sensor 11 c.

The common revolution number is a revolution number which is commonlyset for the fans 3 a and 3 b in order to obtain an air flow rate neededto cool the heating elements 52 a and 52 b in a state in which thedifference in revolution number between the fans 3 a and 3 b ismaintained in the predetermined tolerance as in the case in theheating-element-temperature-based PWM value determination tables 71 a to71 c. In the example illustrated in the drawing, the needed air flowrate stored in the environmental-temperature-based PWM valuedetermination tables 72 a to 72 c is an air flow rate which is obtainedin accordance with an environmental temperature, a system impedance inthe electronic equipment 50 and a total PQ characteristic of the fans 3a and 3 b obtained when a difference in revolution number between thefans 3 a and 3 b is in the predetermined tolerance.

The front-stage PWM value and the rear-stage PWM value are PWM values ofpulses to be input into the front-stage fan 3 a and the rear-stage fan 3b in order to rotate the front-stage fan 3 a and the rear-stage fan 3 bwith a common revolution number as in the case in theheating-element-based PWM value determination tables 71 a to 71 c. Thatis, for example, with the heating element temperature “G”, the pulse ofthe front-stage PWM value “Nfg” is input into the front-stage fan 3 aand the pulse of the rear-stage PWM value “Nrg” corresponding to thefront-stage PWM value “Nfg” is input into the rear-stage fan 3 b torotate the fans 3 a and 3 b with the common revolution number “ggg”.

As described above, the control data storage section 172 corresponds tocontrol data storage means and stores input values of pulses to be inputinto the fans 3 a and 3 b per temperature in order to obtain the airflow rate needed to cool the heating elements in a state in which thedifference in revolution number between the fans 3 a and 3 b ismaintained in the predetermined tolerance. In addition, the control datastorage section 172 corresponds to control data storage means and storesinput values of pulses to be input into the front-stage fan 3 a and therear-stage fan 3 b per system impedance.

As illustrated in FIG. 4, the processor 18 includes an error processingsection 181, a temperature information acquiring section 182, an inputvalue determining section 183 and database preparing section 184.

The error processing section 181 executes an error notifying process onthe basis of information acquired from the revolution number error checksection 14. The error processing section 181 acquires a result of checkindicating that the front-stage fan 3 a or the rear-stage fan 3 b is nowin a stopped state from the revolution number error check section 14.The error processing section 181 then sends an error notification thatthe fan 3 a or 3 b is in the stopped state to the electronic equipment50 on the basis of the result of check acquired. As a result, an errormessage that the fan 3 a or 3 b is now in the stopped state is displayedon a display not illustrated of the electronic equipment 50.

The temperature information acquiring section 182 acquires predeterminedvariables corresponding to temperatures of the heating elements 52 a and52 b from the temperature check sections 12 a and 12 b as dataindicative of the heating element temperatures. The temperatureinformation acquiring section 182 also acquires the environmentaltemperature from the temperature sensor 12 c. As described above, thetemperature sensors 11 a and 11 b, the temperature check sections 12 aand 12 b and the temperature information acquiring section 182 functionsas an example of temperature detecting means for detecting thetemperatures of the heating elements 52 a and 52 b installed in theelectronic equipment 50. The temperature sensor 11 c and the temperatureinformation acquiring section 182 also function as an example oftemperature detecting means for detecting the temperature outside of theelectronic equipment 50.

The input value determining section 183 specifies a system impedancecorresponding to the current configuration of the electronic equipment50 with reference to data stored in the equipment state storage section171. In addition, the input value determining section 183 acquires therespective PWM values of pulses to be input into the fans 3 a and 3 bfrom the control data storage section 172 on the basis of the specifiedsystem impedance and the heating element temperatures or theenvironmental temperature acquired from the temperature informationacquiring section 182.

Specifically, the input value determining section 183 acquires afront-stage PWM value and a rear-stage PWM value corresponding to acombination of the specified system impedance with temperatureinformation of the heating elements 52 a and 52 b acquired from thetemperature information acquiring section 182 from theheating-element-temperature-based PWM value determination tables 71 a to71 c. In addition, the input value determining section 183 acquires afront-stage PWM value and a rear-stage PWM value corresponding to acombination of the specified system impedance with environmentaltemperature information acquired from the temperature informationacquiring section 182 from the environmental-temperature-based PWM valuedetermination tables 72 a to 72 c.

For example, in the case that the specified system impedance is “A” andthe heating element temperature acquired from the temperatureinformation acquiring section 182 is “C”, the input value determiningsection 183 acquires the front-stage PWM value “Nfc” and the rear-stagePWM value “Nrc” from the heating-element-temperature-based PWM valuedetermination table 71 a as illustrated in FIG. 7A.

The input value determining section 183 then instructs the pulsegenerator 15 a to input the pulse of the acquired front-stage PWM valueinto the front-stage blower 3 a and instructs the pulse generator 15 bto input the pulse of the acquired rear-stage PWM value into therear-stage blower 3 b. In response to the instructions, the pulsegenerators 15 a and 15 b respectively input the pulses of thefront-stage PWM value and rear-stage PWM value as instructed from theinput value determining section 183 into the front-stage fan 3 a and therear-stage fan 3 b. As a result, the front-stage fan 3 a rotates withthe revolution number conforming to the front-stage PWM value of thepulse input from the pulse generator 15 a and the rear-stage fan 3 brotates with the revolution number conforming to the rear-stage PWMvalue of the pulse input from the pulse generator 15 b.

Incidentally, as described above, the front-stage PWM value and therear-stage PWM value are PWM values of pulses to be input into the fans3 a and 3 b in order to obtain the needed air flow rate in a state inwhich the difference in revolution number between the fans 3 a and 3 bis maintained in the predetermined tolerance. Therefore, the differencein revolution number between the fans 3 a and 3 b is set in thepredetermined tolerance by inputting pulses of the above mentionedfront-stage and rear-stage PWM values into the respective fans 3 a and 3b and air is fed into the equipment at the needed air flow rateconforming to the temperatures of the heating elements 52 a and 52 b.

As described above, in the fan control device 1 according to thisembodiment, since the difference in revolution number between the fans 3a and 3 b is maintained in the predetermined tolerance, that is, therevolution numbers of the fans 3 a and 3 b are controlled to coincidewith each other in the predetermined tolerance, such a situation may beavoided that surplus noise is generated from a fan of the largestrevolution number to increase the total noise from the fans 3 a and 3 b.

In addition, the needed air flow rate according to this embodiment isdetermined by taking the temperatures of the heating elements 52 a and52 b, the system impedance within the electronic equipment 50 and thetotal PQ characteristic of the fans 3 a and 3 b obtained when thedifference in revolution number between the fans 3 a and 3 b ismaintained in the predetermined tolerance into consideration. Therefore,according to this embodiment, the air flow rate suitable for cooling theheating elements 52 a and 52 b may be obtained in a state in which therevolution numbers of the fans 3 a and 3 b are controlled to coincidewith each other in the predetermined tolerance regardless of theconfiguration of the electronic equipment 50 concerned and the locationsof the fans 3 a and 3 b in the electronic equipment 50.

Incidentally, the input value determining section 183 determinesdifferent PWM values for the front-stage fan 3 a and the rear-stage fan3 b and inputs pulses of the determined PWM values into the fans 3 a and3 b via the pulse generators 15 a and 15 b. That is, as illustrated thegraph 1001 in FIG. 8, different amounts of energy 1010 are supplied tothe front-stage fan 3 a and the rear-stage fan 3 b. Specifically, thework amount of the rear-stage fan 3 b is reduced influenced by the aircurrents generated from the front-stage fan 3 a, so that the amount ofenergy supplied to the rear-stage fan 3 b becomes smaller than thatsupplied to the front-stage fan 3 a in the case that the revolutionnumbers of the fans 3 a and 3 b are controlled to coincide with eachother.

In addition, in the case that the common revolution number obtained onthe basis of the environmental temperature is larger than the commonrevolution number obtained on the basis of the heating elementtemperatures, the input value determining section 183 controls therevolutions numbers of the fans 3 a and 3 b by using theenvironmental-temperature-based PWM values. Specifically, the inputvalue determining section 183 acquires common revolution numberscorresponding to the environmental temperature and the heating elementtemperatures acquired from the temperature information acquiring sectionrespectively from the environmental-temperature-based PWM determinationtables 72 a to 72 c and the heating-element-temperature-based PWM valuedetermination tables 71 a to 71 c. The input value determining section183 then compares a common revolution number obtained from theenvironmental temperature with a common revolution number obtained fromthe heating element temperatures, and in the case that the commonrevolution number obtained from the environmental temperature is largerthan that obtained from the heating element temperatures, acquires thefront-stage PWM value and the rear-stage PWM value corresponding to theenvironmental temperature concerned from theenvironmental-temperature-based PWM value determination tables 72 a to72 c. As described above, the revolution numbers of the fans 3 a and 3 bare controlled on the basis of one of the environmental temperature andthe heating element temperatures which will influence the heatingelements 52 a and 52 b more greatly than another, so that the heatingelements 52 a and 52 b may be maintained at more appropriatetemperatures.

As described above, the input value determining section 183 and theequipment state storage section 171 function as an example of equipmentstate acquiring means for acquiring information on the system impedancewithin the electronic equipment 50. In addition, the input valuedetermining section 183 and the pulse generators 15 a and 15 b functionas an example of control means for controlling the revolution number ofeach fan on the basis of the temperature information acquired using thetemperature information acquiring section 182 such that the air flowrate of air for cooling the heating elements 52 a and 52 b which isdetermined in accordance with the temperatures of the heating elements52 a and 52 b, the system impedance within the electronic equipment 50and the total static pressure-air flow rate characteristic of the fans 3a and 3 b attained when the difference in revolution number between thefans 3 a and 3 b is maintained in the predetermined tolerance may beobtained and the difference in revolution number between the fans 3 aand 3 b may be set in the predetermined tolerance.

The database preparing section 184 executes various calculatingprocesses in order to prepare the heating-element-temperature-based PWMvalue determination tables 71 a to 781 c and theenvironmental-temperature-based PWM value determination tables 72 a to72 c before the fan control device is incorporated into the electronicequipment 50. Next, a specific configuration of the database preparingsection 184 will be described. FIG. 9 is a block diagram illustrating aspecific configuration of the database preparing section according tothe embodiment 2.

As illustrated in FIG. 9, the database preparing section 184 includes ameasured (already measured) system impedance information storage section81, an equipment configuration information storage section 82, a systemimpedance information storage section 83, a temperature informationstorage section 84 and a temperature standard value information storagesection 85. The database preparing section 184 also includes a neededair flow rate information storage section 86, a measured (alreadymeasured) PQ characteristic information storage section 87, a PQcharacteristic information and revolution number information storagesection 88 and a PWM value information storage section 89. The databasepreparing section 184 further includes a system impedance calculatingsection 91, a needed air flow rate calculating section 92, a fan PQperformance calculating section 93 and a fan PWM value calculatingsection 94.

The measured system impedance information storage section 81 storesmeasured system impedances of the electronic equipment 50. For example,the measured system impedance information storage section 81 storessystem impedances corresponding to full configurations and popularconfigurations of the electronic equipment 50. The equipmentconfiguration information storage section 82 stores a plurality ofpatterns of configurations of the electronic equipment 50. For example,the equipment configuration information storage section 82 storesinformation on the number of CPUs and the number of power sources whichare built into the electronic equipment 50 per configuration of theelectronic equipment 50. The system impedance information storagesection 83 stores system impedances which are calculated perconfiguration of the electronic equipment 50 using the system impedancecalculating section 91.

The temperature information storage section 84 stores the environmentaltemperature and the temperatures of the heating elements 5 a and 52 b.For example, the temperature information storage section 84 stores thetemperatures of the CPUs and memories built into the electronicequipment as the temperatures of the heating element 52 a and 52 b. Thetemperature standard value information storage section 85 storesstandard values of temperatures of the heating elements 52 a and 52 b.The needed air flow rate information storage section 86 stores theneeded air flow rates calculated using the needed air flow ratecalculating section 92.

The measured PQ characteristic information storage section 87 stores theinformation on the maximum and minimum revolution numbers of the fans 3a and 3 b. The PQ characteristic information and revolution numberinformation storage section 88 stores the total PQ characteristic of thefans 3 a and 3 b and the common revolution numbers of the fans 3 a and 3b calculated using the fan PQ performance calculating section 93. ThePWM value information storage section 89 stores the front-stage PWMvalues and rear-stage PWM values calculated using the fan PWM valuecalculating section 94.

The system impedance calculating section 91 calculates each systemimpedance of each configuration of the electronic equipment 50 on thebasis of the information on the measured system impedances stored in themeasured system impedance information storage section 81 and theinformation on the configurations of the electronic equipment 50 storedin the equipment configuration information storage section 82. Theneeded air flow rate calculating section 92 calculates the needed airflow rates on the basis of the temperatures stored in the temperatureinformation storage section 84 and the temperature standard valuesstored in the temperature standard value information storage section 85.

The fan PQ performance calculating section 93 calculates the total PQcharacteristic of the fans 3 a and 3 b and the common revolution numbersof the fans 3 a and 3 b. The calculation is performed on the basis ofinformation on the system impedances stored in the system impedanceinformation storage section 83, the needed air flow rates stored in theneeded air flow rate information storage section 86 and the maximum andminimum revolution numbers of the fans 3 a and 3 b stored in themeasured PQ characteristic information storage section 87. The fan PWMvalue calculating section 94 calculates the front-stage PWM values andrear-stage PWM values. The calculation is performed on the basis ofinformation on the maximum and minimum revolution numbers of the fans 3a and 3 b stored in the measured PQ characteristic information storagesection 87 and the total PQ characteristic of the fans 3 a and 3 b andthe common revolution numbers of the fans 3 a and 3 b stored in the PQcharacteristic information and revolution number information storagesection 88.

Next, procedures of preparing the heating-element-temperature-based PWMvalue determination tables 71 a to 71 c and theenvironmental-temperature-based PWM value determination tables 72 a to72 c will be described. FIG. 10 is a flowchart illustrating an exampleof procedures of preparing the heating-element-temperature-based PWMvalue determination tables 71 a to 71 c and theenvironmental-temperature-based PWM value determination tables 72 a to72 c.

As illustrated in FIG. 10, as work to be previously performed inpreparation of the heating-element-temperature-based PWM valuedetermination tables 71 a to 71 c and theenvironmental-temperature-based PWM value determination tables 72 a to72 c, first, measurement and simulation are performed (step S101).Specifically, system impedances corresponding to the full and popularconfigurations of the electronic equipment, and maximum and minimumrevolution numbers, air flow rates, static pressures and noise levels ofthe fans 3 a and 3 b are obtained by the measurement and simulation.

Next, various calculations are performed on the basis of the informationobtained at step S101 using the database preparing section 184 (stepS102). Specifically, each system impedance of each equipmentconfiguration and each needed air flow rate, each common revolutionnumber, each front-stage PWM value and each rear-stage PWM value at eachtemperature are calculated (step 102).

Then, each system impedance calculated for each equipment configurationand each needed air flow rate, each common revolution number, eachfront-stage PWM value and each rear-stage PWM value which are calculatedat each of the environmental temperature and the heating elementtemperatures are arranged in the form of databases and stored in the ROM17 (step S103). Owing to the above mentioned operations, theheating-element-temperature-based PWM value determination tables 71 a to71 c and the environmental-temperature-based PWM value determinationtables 72 a to 72 c are stored in the ROM 17. The fan control device 1is then incorporated into the electronic equipment 50 in a state inwhich the heating-element-temperature-based PWM value determinationtables 71 a to 71 c and the environmental-temperature-based PWM valuedetermination tables 72 a to 72 c are stored in the ROM 17.

Next, specific operations of the processor 18 according to thisembodiment will be described. FIG. 11 is a flowchart illustrating anexample of procedures of processing executed using the processoraccording to the embodiment 2. Incidentally, only a procedure involvingrevolution number control of the front-stage fan 3 a and the rear-stagefan 3 b of the procedures of processing executed using the processor 18is illustrated in FIG. 11.

As illustrated in FIG. 11, first, the input value determining section183 acquires an equipment state (step S201). Specifically, the inputvalue determining section 183 specifies a system impedance to which anequipment state specification flag is set as the system impedancecorresponding to the current configuration of the electronic equipment50 with reference to data stored in the equipment state storage section171.

Next, the input value determining section 183 selects a databasecorresponding to the specified system impedance (step S202).Specifically, the input value determining section 183 selects oneheating-element-temperature-based PWM value determination table fromwithin the heating-element-temperature-based PWM value determinationtables 71 a to 71 c and one environmental-temperature-based PWM valuedetermination table from within the environmental-temperature-based PWMvalue determination tables 72 a to 72 c.

Next, the processor 18 executes temperature measurement (step S203).Specifically, the temperature information acquiring section 182 acquirespredetermined variables corresponding to temperatures of the heatingelements 52 a and 52 b from the temperature check sections 12 a and 12 bas heating element temperatures and acquires an environmentaltemperature from the temperature sensor 12 c. The temperatureinformation acquiring section 182 then notifies the input valuedetermining section 183 of the acquired heating element andenvironmental temperatures.

Next, the input value determining section 183 selects a commonrevolution number corresponding to the heating element temperaturesacquired at step S203 with reference to theheating-element-temperature-based PWM determination table (step S204).The input value determining section 183 also selects a common revolutionnumber corresponding to the environmental temperature acquired at stepS203 with reference to the environmental-temperature-based PWM valuedetermination table (step S205).

Next, the input value determining section 183 judges whether theheating-element-temperature-based common revolution number is largerthan the environmental-temperature-based common revolution number (stepS206). In the above mentioned process, in the case that it has beenjudged that the common revolution number obtained from the heatingelement temperature is larger than the common revolution number obtainedfrom the environmental temperature (Yes at step S206), the input valuedetermining section 183 determines the PWM values of pulses to be inputinto the fans 3 a and 3 b using the heating-element-temperature-basedPWM value determination table 71.

Specifically, the input value determining section 183 determines thefront-stage PWM value corresponding to the common revolution numberselected at step S204 with reference to theheating-element-temperature-based PWM value determination table 71 (stepS207). The input value determining section 183 then determines therear-stage PWM value corresponding to the front-stage PWM value withreference to the heating-element-temperature-based PWM valuedetermination table 71 (step S208). For example, in the case that thecurrent system impedance of the electronic equipment 50 is “A” and theheating element temperature acquired using the temperature informationacquiring section 182 is “C”, the input value determining section 183selects the common revolution number “ccc” with reference to theheating-element-temperature-based PWM value determination table 71 aillustrated in FIG. 7A. Then, the input value determining section 183determines the front-stage PWM value “Nfc” and the rear-stage PWM value“Nrc” corresponding to the common revolution number “ccc” as the PWMvalues of the pulses to be input into the fans 3 a and 3 b.

On the other hand, at step S204, it has been judged that theheating-element-temperature-based common revolution number is not largerthan the environmental-temperature-based common revolution number (No atstep S206); the input value determining section 183 determines the PWMvalues of pulses to be input into the fans 3 a and 3 b by using theheating-element-temperature-based PWM value determination table 71.

Specifically, the input value determining section 183 determines afront-stage PWM value corresponding to the common revolution numberselected at step S205 with reference to theenvironmental-temperature-based PWM value determination table 72 (stepS209). The input value determining section 183 determines a rear-stagePWM value corresponding to the front-stage PWM value with reference tothe heating-element-temperature-based PWM value determination table 71(step S210). For example, in the case that the current system impedanceof the electronic equipment 50 is “A” and the environmental temperatureacquired using the temperature information acquiring section 182 is “G”,the input value determining section 183 selects the common revolutionnumber “ggg” with reference to the environmental-temperature-based PWMvalue determination table 72 a as illustrated in FIG. 7B. The inputvalue determining section 183 then determines the front-stage PWM value“Nfg” and the rear-stage PWM value “Nrg” corresponding to the commonrevolution number “ggg” as the PWM values of pulses to be input into thefans 3 a and 3 b.

At the completion of execution of the process at step S208 or step S210,the input value determining section 183 instructs to rotate the fans(step S211). That is, the input value determining section 183 instructsthe pulse generators 15 a and 15 b to input pulses of the front-stageand rear-stage PWM values determined at steps S207 and S208 or at stepsS209 and S210 respectively into the front-stage fan 3 a and therear-stage fan 3 b. In response to the instruction, the pulse generator15 a inputs the pulse of the above front-stage PWM value into thefront-stage fan 3 a as instructed from the input value determiningsection 183. Likewise, the pulse generator 15 b inputs the pulse of theabove rear-stage PWM value into the rear-stage fan 3 b as instructedfrom the input value determining section 183. As a result, thefront-stage fan 3 a and the rear-stage fan 3 b rotate with therevolution numbers corresponding to the front-stage PWM value and therear-state PWM value which have been input from the pulse generators 15a and 15 b.

Incidentally, as described above, the front-stage PWM value and therear-stage PWM value are PWM values of pulses to be input into the fans3 a and 3 b in order to obtain the needed air flow rate in a state inwhich the difference in revolution number between the fans 3 a and 3 bis maintained in the predetermined tolerance. Therefore, the fans 3 aand 3 b rotate in a state in which the revolution numbers of the fanscoincide with each other in the predetermined tolerance by inputting thepulses of the above front-stage and rear-stage PWM values respectivelyinto the fans 3 a and 3 b and air is fed into the heating elements 52 aand 52 b at the needed air flow rates conforming to the temperatures ofthe heating elements 52 a and 52 b.

FIG. 12 is a diagram illustrating an effect of the embodiment. In FIG.12, a left part is a graph indicative of changes in static pressure,revolution number and noise relative to a change in air flow rateobtained when the PWM values of the pulses applied to the front-stagefan 3 a and the rear-stage fan 3 b are made the same as each other at apredetermined temperature.

As illustrated in the graph, in the case that pulses of the same PWMvalue have been applied to the fans 3 a and 3 b, if it is intended toobtain a needed air flow rate 3003 at which the total aerodynamicperformance 3001 of the fans 3 a and 3 b intersects the system impedance3002, the revolution number of the rear-stage fan 3 b (the rear-stagerevolution number 3004B) will become larger than the revolution numberof the front-stage fan 3 a (the front-stage revolution number 3004A).The reason therefore lies in the fact that the work amount with whichthe rear-stage fan 3 b blows off air is reduced under the influence ofthe air currents generated from the front-stage fan 3 a to increase therevolution number of the rear-stage fan 3 b. The noise 3005 is alsoincreased with increasing the revolution number of the rear-stage fan 3b.

On the other hand, in FIG. 12, a right part is a graph indicative ofchanges in static pressure, revolution number and noise relative to achange in air flow rate obtained in the case that the fan control device1 according to this embodiment has controlled such that the differencein revolution number (4004A, 4004B) between the front-stage fan 3 a andthe rear-stage fan 3 b is maintained in the predetermined tolerance at apredetermined temperature. As illustrated in this graph, according tothis embodiment, it may become possible to obtain the needed air flowrate 4003 at which the system impedance 4002 within the electronicequipment 50 intersects the total aerodynamic characteristic 4001 (thePQ characteristic) of the fans 3 a and 3 b when the difference inrevolution number between the fans 3 a and 3 b is maintained in thepredetermined tolerance in a state in which the difference in revolutionnumber between the fans is set in the predetermined tolerance at thepredetermined temperature.

Therefore, according to this embodiment, such a situation may be avoidedthat the revolution number of any one of the fans becomes larger thanthat of another fan to generate surplus noise. In addition, according tothis embodiment, the air flow rate suited to cool the heating elements52 a and 52 b may be obtained in a state in which the difference inrevolution number between the fans 3 a and 3 b is maintained in thepredetermined tolerance regardless of the configuration of theelectronic equipment 50 and the locations of the fans 3 a and 3 b withinthe electronic equipment 3 a and 3 b.

Next, results of experiments performed to validate that the noisegenerated from the plurality of fans 3 a and 3 b is reduced by using thefan control device 1 according to this embodiment will be described.Respective measurement conditions 3010 are illustrated in FIG. 13. FIG.13 illustrates measurement conditions of the experiments for validation.As illustrated in FIG. 13, a case in which two fans of the same type aredisposed in series is assumed to be a measurement condition A and a casein which two fans of the same type are disposed in series and four fansof the same type are disposed in parallel is assumed to be a measurementcondition B.

Under the measurement condition A, experiments were performed underthree conditions of conditions A-1 to A-3. Specifically, under thecondition A-1, voltages of the same amount were supplied to thefront-stage and rear-stage fans. Under the condition A-2, the same airflow rate as that under the condition A-1 was set and voltages werecontrolled such that the ratio of the front-stage fan revolution numberto the rear-stage fan revolution number is 1:1. The condition A-2corresponds to a condition under which the same control as thatperformed using the fan control device 1 according to this embodiment isperformed. Under the condition A-3, the same air flow rate at that underthe condition A-1 was set and voltages were controlled such that theratio of the front-stage fan revolution number to the rear-stage fanrevolution number is 1:0.9.

In addition, as illustrated in FIG. 13, under the measurement conditionB, experiments were performed under four conditions of conditions B-1,B-2, B-3 and B-4. Specifically, under the condition B-1, voltages of thesame amount were supplied to the front-stage and rear-stage fans. Underthe condition B-2, the same air flow rate as that under the conditionB-1 was set and voltages were controlled such that the ratio of thefront-stage fan evolution number to the rear-stage fan revolution numberis 1:1. The condition B-2 corresponds to a condition under which thesame control as that performed using the fan control device 1 accordingto this embodiment is performed.

Under the condition B-3, voltages of the same amount which is differentfrom that of the voltages supplied under the condition B-1 were suppliedto the front-stage and rear-stage fans. Under the condition B-4, thesame air flow rate as that under the condition B-3 was set and voltageswere controlled such that the ratio of the front-stage fan revolutionnumber to the rear-stage fan revolution number is 1:1. The condition B-4corresponds to a condition under which the same control as thatperformed using the fan control device 1 according to this embodiment isperformed.

First, results of measurements performed under the measurement conditionA will be described. FIG. 14A illustrates data indicative of the resultof measurement of the front-stage fan revolution number 5001A, therear-stage fan revolution number 5001B and the device noise 5002performed under the measurement condition A. FIG. 14B illustrates dataindicative of the result of measurement of the front-stage fanrevolution number 6001A, the rear-stage fan revolution number 6001B andthe consumption power 6002 performed under the measurement condition A.FIG. 14C illustrates data indicative of the result of frequency analysisof the device noise performed under the measurement condition A. FIG.15A is a diagram 3020A illustrating a result of measurement performedunder the condition A-1, FIG. 15B is a diagram 3020B illustrating aresult of measurement performed under the condition A-2 and FIG. 15C isa diagram 3020C illustrating a result of measurement performed under thecondition A-3.

As illustrated in FIGS. 14A and 15A, under the condition A-1, thefront-stage revolution number 5001A was 12257 min⁻¹ and the rear-stagerevolution number 5001B was 13523 min⁻¹, indicating that in the casethat voltages of the same amount have been supplied to the front-stageand rear-stage fans, the rear-stage fan revolution number 5001B isincreased influenced by air currents generated from the front-stage fan.As illustrated in FIGS. 14A and 15C, under the condition A-3, thefront-stage revolution number was 13643 min⁻¹ and the rear-stagerevolution number was 12277 min⁻¹, indicating that the front-stage fanrevolution number measured under the condition A-3 is larger than therear-stage fan revolution number measured under the condition A-1. Onthe other hand, as illustrated in FIGS. 14B and 15B, under the conditionA-2, the front-stage revolution number was 12615 min⁻¹ and therear-stage revolution number was 12555 min⁻¹, indicating that theserevolution numbers are smaller than the rear-stage revolution numbermeasured under the condition A-1 and the front-stage revolution numbermeasured under the condition A-3.

In addition, as illustrated in FIG. 14A and FIGS. 15A to 15C, the devicenoise 5002 measured under the condition A-1 was 55.5 dB (A), the devicenoise 5002 measured under the condition A-2 was 53.4 dB(A) and thedevice noise 5002 measured under the condition A-3 was 56 dB(A). Thatis, the device noise was the lowest when measured under the conditionA-2 corresponding to a control system of the fan control device 1according to this embodiment and was reduced from the value measuredunder the condition A-1 by about 2 dB(A). On the other hand, the highestdevice noise 5002 was measured under the condition A-3. It is thoughtthat the reason therefore lies in the fact that the front-stagerevolution number 5001A measured under the condition A-3 exhibited thehighest value of the values measured under the respective conditions A-1to A-3.

As described above, the noise generated from each fan may be reduced bycontrolling so as to attain a needed air flow rate in a state in whichthe revolution numbers of the front-stage and rear-stage fans (5001A,5001B) are controlled to coincide with each other in the predeterminedtolerance as in the case with the fan control device 1 according to thisembodiment. Incidentally, the device noise 5002 under each of theconditions A-1 to A-3 is of a value calculated on the basis of theresult of analysis of the frequency of the device noise illustrated inFIG. 14C.

In addition, as illustrated in FIG. 14B and FIGS. 15A to 15C, the totalconsumption power 5003 of the front-stage and rear-stage fans was 7.20 Wunder the condition A-1, was 6.78 W under the condition A-2 and was 7.65W under the condition A-3. That is, as in the case of the device noise5002 the total consumption power 5003 was also the lowest when measuredunder the condition A-2 corresponding to that of the control system ofthe fan control device 1 according this embodiment and was reduced fromthe value measured under the condition A-1 by about 6%. As describedabove, the consumption power 5003 of each fan may be reduced bycontrolling so as to attain the needed air flow rate in a state in whichthe revolution numbers of the front-stage and rear-stage fans (5001A,5001B) are controlled to coincide with each other in the predeterminedtolerance as in the case with the fan control device 1 according to thisembodiment.

Next, results of measurements performed under the measurement conditionB will be described. First, the results of measurements performed underthe conditions B-1 and B-2 will be described. FIG. 16A illustrates dataindicative of the result of measurement of the front-stage averagerevolution number 7001A, the rear-stage average revolution number 7002Aand the device noise 7003 performed under the conditions B-1 and B-2.FIG. 16B illustrates data indicative of the result of measurement of thefront-stage average revolution number 7001A, the rear-stage averagerevolution number 7001B and the consumption power 7003 performed underthe conditions B-1 and B-2. FIG. 16C illustrates data indicative of theresult of frequency analysis of the device noise 7002 performed underthe conditions B-1 and B-2. FIG. 17A is a diagram 3030 illustrating theresult of measurement performed under the condition B-1 and FIG. 17B isa diagram 3040 illustrating the result of measurement performed underthe condition B-2. In the examples illustrated in the drawings, thefront-stage average revolution number 7001A is the average value ofrevolution numbers of four front-stage fans and the rear-stage averagerevolution number 7001B is the average value of revolution numbers offour rear-stage fans.

As illustrated in FIGS. 16A and 17A, the front-stage average revolutionnumber 7001A was 14488 min⁻¹ and the rear-stage average revolutionnumber 7001B was 15548 min⁻¹ under the condition B-1. These valuesindicate that in the case that the voltages of the same amount have beensupplied to the front-stage fan and the rear-stage fan as in the caseunder the condition A-1, the revolution number of the rear-stage fan7001B is increased influenced by the air currents generated from thefront-stage fan. On the other hand, as illustrated in FIGS. 16A and 17B,the front-stage average revolution number 7001A was 14825 min⁻¹ and therear-stage average revolution number 7001B was 14859 min⁻¹ under thecondition B-2. These revolution numbers 7001A, 7001B are smaller thanthe rear-stage average revolution number measured under the conditionB-1.

As illustrated in FIG. 16A and FIGS. 17A and 17B, the device noise 7002under the condition B-1 was 62.6 dB(A) and the device noise 7002 underthe condition B-2 was 61.6 dB(A). That is, as in the case under themeasurement condition A, the device noise 7002 measured under thecondition B-2 which is the same as that of the fan control device 1according to this embodiment was lower than that measured under thecondition B-1 and was reduced from the value measured under thecondition B-1 by about 1 db(A).

As described above, even when the front-stage fans and the rear-stagefans are disposed in series and in parallel, an effect equivalent tothat attained when the front-stage fan and the rear-stage fan aredisposed only in series is obtained. Incidentally, the values of thedevice noise illustrated in FIG. 16A were calculated on the basis of theresult of analysis of the frequency of the device noise 7002 illustratedin FIG. 16C.

In addition, as illustrated in FIG. 16B and FIGS. 17A and 17B, the totalconsumption power 7003 of the front-stage and rear-stage fans was 43.08W under the condition B-1 and was 41.83 W under the condition B-2. Thatis, the total consumption power 7003 was the lowest when measured underthe condition B-2 corresponding to that of the fan control device 1according to this embodiment and was reduced from the value measuredunder the condition B-1 by about 3%.

Next, results of measurements performed under the conditions B-3 and B-4will be described. FIG. 18A illustrates data indicative of the result ofmeasurement of the front-stage average revolution number 8001A, therear-stage average revolution number 8001B and the device noise 8002performed under the conditions B-3 and B-4, FIG. 18B illustrates dataindicative of the result of measurement of the front-stage averagerevolution number 8001A, the rear-stage average revolution number 8001Band the consumption power 8003 performed under the conditions 18-3 and18-4 and FIG. 18C illustrates data indicative of the result of analysisof the frequency of the device noise 8002 performed under the conditionsB-3 and B-4. FIG. 19A is a diagram 3050 illustrating the result ofmeasurement performed under the condition B-3 and FIG. 19B is a diagram3060 illustrating the result of measurement performed under thecondition B-3.

As illustrated in FIGS. 18A and 19A, under the condition B-3, thefront-stage average revolution number 8001A was 12576 min⁻¹ and therear-stage average revolution number was 13354 min⁻¹. This result is thesame as those attained under the conditions A-1 and B-1. On the otherhand, as illustrated in FIGS. 18A and 19B, under the condition B-4, thefront-stage average revolution number was 12826 min⁻¹ and the rear-stageaverage revolution number 8001B was 12809 min⁻¹. That is, these valuesare smaller than the value of the rear-stage average revolution number8001B measured under the condition B-3.

As illustrated in FIG. 18A and FIGS. 19A and 19B, the device noise 8002under the condition B-3 was 58.7 db(A) and the device noise 8002 underthe condition B-4 was 57.7 dB(A). That is, the device noise 8002measured under the condition B-4 which is the same as that of the fancontrol device 1 according to this embodiment was lower than thatmeasured under the condition B-3 and was reduced from the value measuredunder the condition B-3 by about 1 db(A) as in the case in the relationbetween the conditions B-1 and B-2.

As described above, it has been found that even when the air flow ratesof air generated from each front-stage fan and each rear-stage fan arevaried, the same result may be obtained by changing the amount ofvoltages applied in the case that the front-stage fans and therear-stage fans are disposed in series and in parallel. Incidentally,the values of the device noise illustrated in FIG. 18A are calculated onthe basis of the result of analysis of the frequency of the device noiseillustrated in FIG. 18C.

As illustrated in FIG. 18B and FIGS. 19A and 19B, the total consumptionpower 8003 of the front-stage and rear-stage fans was 27.80 W under thecondition B-3 and was 26.87 W under the condition B-4. That is, thetotal consumption power 8003 was also the lowest when measured under thecondition B-4 which is the same as that of the fan control device 1according to this embodiment as in the case in the relation between theconditions B-1 and B-2 and was reduced from the value measured under thecondition B-3 by about 3%.

As described above, according to the embodiment 2, the air flow rate ofair cooling the heating elements 52 a and 52 b which is determined fromthe temperatures of the heating elements 52 a and 52 b, the systemimpedance within the electronic equipment 50 and the total PQcharacteristic of the fans 3 a and 3 b attained in a state in which thedifference in revolution number between the fans 3 a and 3 b ismaintained in the predetermined tolerance is obtained. In addition, therevolution number of each of the fans 3 a and 3 b is controlled on thebasis of the temperatures of the heating elements and the environmentaltemperature such that the difference in revolution number between thefans 3 a and 3 b is set in the predetermined tolerance. That is, in theembodiment 2, the revolution number of each of the fans 3 a and 3 b iscontrolled on the basis of the heating element temperatures and theenvironmental temperature such that the needed air flow rate which isneeded for cooling the heating elements 52 a and 52 b and is determinedfrom the temperatures of the heating elements 52 a and 52 b, the systemimpedance within the electronic equipment 50 and the total PQcharacteristic of the fans 3 a and 3 b obtained in a state in which therevolution numbers of the fans 3 a and 3 b are controlled to coincidewith each other in the predetermined tolerance may be obtained in astate in which the revolution numbers of the fans 3 a and 3 b coincidewith each other in the predetermined tolerance.

That is, according to this embodiment, such a situation that the totalnoise generated from the fans 3 a and 3 b owing to the surplus noisegenerated from the fan of the largest revolution number may be avoidedby maintaining the difference in revolution number between the fans 3 aand 3 b in the predetermined tolerance. In addition, in this embodiment,the needed air flow rate may be obtained by taking the temperatures ofthe heating elements 52 a and 52 b, the system impedance within theelectronic equipment 50 and the total PQ characteristic of the fans 3 aand 3 b obtained in a state in which the difference in evolution numberbetween the fans 3 a and 3 b is in the predetermined tolerance intoconsideration. Therefore, according to this embodiment, the air flowrate suited to cool the heating elements 52 a and 52 b may be obtainedin a state in which the difference in revolution number between the fans3 a and 3 b is maintained in the predetermined tolerance regardless ofthe configuration of the electronic equipment 50 concerned and thelocations of the respective fans 3 a and 3 b within the electronicequipment 50.

As described above, according to this embodiment, the noise generatedfrom the plurality of fans 3 a and 3 b may be reduced while attainingthe air flow rate needed for cooling the heating elements 52A and 52Bwithin the electronic equipment 50 using the plurality of fans 3 a and 3b.

In addition, according to this embodiment, the revolution number of therear-stage fan 3 b is reduced more remarkably than that attained whenthe energy of the same amount is supplied to the both fans 3 a and 3 band hence the service life of the rear-stage fan 3 b may be increased.Further, according to this embodiment, addition of components is notneeded and hence the above mentioned effects may be realized at a costequivalent to an ever attained cost.

Incidentally, a fan control program is stored in the ROM 17 of the fancontrol device 1 and functions as mentioned above are implemented byexecuting this fan control program using the processor 18. Next, anexample of a computer for executing the fan control program will beillustrated. FIG. 20 is a functional block diagram illustrating acomputer for executing the fan control program.

As illustrated in FIG. 20, a computer 600 serving as the fan controldevice 1 includes an HDD 610, a RAM 620, a ROM 630, a CPU 60 and a bus650 for connecting these elements with one another. The ROM 630corresponds to the ROM 17 illustrated in FIG. 2 and stores in advancethe fan control program. The fan control program includes a temperaturedetection program 631 and a control program 632.

Then, the CPU 640 reads the temperature detection program 631 and thecontrol program 632 out of the ROM 630 and executes these programs. As aresult of execution of these programs, the programs 631 and 632 come tofunction respectively as a temperature detection process 641 and acontrol process 642. As described above, the CPU 640 corresponds to theprocessor 18 in FIG. 2.

The ROM 630 includes the equipment state storage section 171 and thecontrol data storage section 172 and stores the equipment statemanagement table 61, the heating-element-temperature-based PWM valuedetermination tables 71 a to 71 c and theenvironmental-temperature-based PWM value determination tables 72 a to72 c in these storage sections. The CPU 640 reads these tables stored inthe ROM 630 and stores these tables in the RAM 620 such that theprocesses 641 and 642 execute various processes utilizing the datastored in the RAM 620.

Embodiment 3

Although, in the above mentioned embodiment 2, the evolution numbers ofthe fans 3 a and 3 b detected using the revolution number detectingsections 13 a and 13 b are used only for revolution number error check,the revolution numbers of the fans 3 a and 3 b may be utilized asfeedback information used to set the difference in revolution numberbetween the fans 3 a and 3 b in the predetermined tolerance. Next, anembodiment involving a case as mentioned above will be described. FIG.21 is a block diagram illustrating a configuration of a fan controldevice according to an embodiment 3. Incidentally, the same numerals areassigned to parts having the same configurations as those previouslydescribed and description thereof will be omitted.

As illustrated in FIG. 21, in a fan control device 1′ according to thisembodiment, a processor 18′ acquires information on the revolutionnumbers of the fans 3 a and 3 b from the revolution number detectingsections 13 a and 13 b. Next, specific configurations of the processor18′ and a ROM 17′ according to this embodiment will be described hereinbelow. FIG. 22 is a block diagram illustrating specific configurationsof the processor 18′ and the ROM 17′ according to the embodiment 3.

As illustrated in FIG. 22, the processor 18′ according to thisembodiment includes the error processing section 181, the temperatureinformation acquiring section 182, an input value determining section183′, the database preparing section 184 and a revolution numberinformation acquiring section 185. The revolution number informationacquiring section 185 acquires information on the revolution numbers ofthe front-stage fan 3 a and the rear-stage fan 3 b respectively from therevolution number detecting sections 13 a and 13 b. As described above,the revolution number information acquiring section 185 and therevolution number detecting section 13 a function as an example offront-stage revolution number detecting means for detecting therevolution number of the front-stage fan 3 a and the revolution numberinformation acquiring section 185 and the revolution number detectingsection 13 a functions as an example of rear-stage revolution numberdetecting means for detecting the revolution number of the rear-stagefan 3 b.

The input value detecting section 183′ then performs feedback control onthe revolution number of the rear-stage fan 3 b on the basis ofinformation acquired from the revolution number information acquiringsection 185. Specifically, in the case that a difference in revolutionnumber between the front-stage fan 3 a and the rear-stage fan 3 b is outof a predetermined tolerance, the input value determining section 183′changes the revolution number of the rear-stage fan such that thedifference in revolution number between the front-stage fan 3 a and therear-stage fan 3 b is set in the predetermined tolerance. Processing asmentioned above is executed with reference to a rear-stage PWM valuechange table stored in a control data storage section 172′.

The control data storage section 172′ according to this embodimentstores a PWM value for the rear-stage fan 3 b obtained when a differencein evolution number between the front-stage fan 3 a and the rear-stagefan 3 is reduced to have a value in the predetermined tolerance perrevolution number. Next, information stored in the control data storagesection 172′ will be described. FIG. 23 is a diagram illustratinginformation stored in the control data storage section according to theembodiment 3.

As illustrated in FIG. 23, rear-stage PWM value change tables 73 a to 73c corresponding to the system impedances A to C are stored in thecontrol data storage section 172′ according to this embodiment inaddition to the heating-element-temperature-based PWM valuedetermination tables 71 a to 71 c and theenvironmental-temperature-based PWM value determination tables 72 a to72 c. FIG. 24 illustrates an example of the rear-stage PWM change table73 a.

As illustrated in FIG. 24, in the rear-stage OWM value change table 73a, each front-stage revolution number indicative of the revolutionnumber of each front-stag fan 3 a is stored corresponding to eachrear-stage PWM value. For example, in the rear-stage PWM value changetable 73 a, the front-stage revolution number “jjj” is storedcorresponding to the rear-stage PWM value “Nrj”.

The rear-stage PWM value stored in the rear-stage PWM value change table3 a is a PWM value needed to control the revolution number of therear-stage fan 3 b to have a difference relative to the evolution numberof the front-stage fan 3 a in a predetermined tolerance. That is, forexample, in the case that the revolution number “kkk” of the front-stagefan 3 a has been acquired from the revolution number informationacquiring section 185, the input value determining section 183′determines the rear-stage PWM value “Nrk” corresponding to the acquiredrevolution number with reference to the rear-stage PWM value changetable 73 a. The input value determining section 183′ then inputs thepulse of the determined rear-stage PWM value “Nrk” into the rear-stagefan 3 b via the pulse generator 15 b. Owing to the above mentionedoperations, even when the revolution number of the front-stage fan 3 adiffers from the revolution number of the rear-stage fan 3 b, the fancontrol device 1′ will be capable of performing correction such that thedifference in revolution number between these fans is set in thepredetermined tolerance.

Next, specific operations of the processor 18′ according to thisembodiment will be described. FIG. 25 is a flowchart illustrating anexample of processing executed using the processor 18′ according to theembodiment 3. Incidentally, in FIG. 25, in procedures of processingexecuted using the processor 18′, only a procedure of processinginvolving control of the revolution numbers of the front-stage andrear-stage fans 3 a and 3 b will be described. Processes executed atsteps S301 to S311 in FIG. 25 are the same as the processes executed atsteps S201 to S211 in FIG. 11 and hence description thereof will beomitted.

As illustrated in FIG. 25, after an instruction to rotate the fans 3 aand 3 b has been given at step S311, the input value determining section183′ measures the revolution numbers of the fans (step S312).Specifically, the input value determining section 183′ acquiresinformation on the revolution numbers of the front-stage and rear-stagefans 3 a and 3 b from the revolution number information acquiringsection 185.

Next, the input value determining section 183′ judges whether adifference in revolution number between the front-stage and rear-stagefans is in a predetermined tolerance (step S313). In the case that ithas been judged that the difference in revolution number between thefans is in the predetermined tolerance in execution of the abovementioned process (Yes at step S313), the input value determiningsection 183′ shifts the process to step S312.

On the other hand, in the case that the difference in revolution numberbetween the fans is not in the predetermined tolerance (No at stepS313). The input value determining section 183′ changes the rear-stagePWM value (step S314). Specifically, the input value determining section183′ determines, on the basis of information on the revolution number ofthe front-stage fan 3 a acquired from the revolution number acquiringsection 185, the rear-state PWM value corresponding to the acquiredrevolution number of the front-stage fan 3 a with reference to therear-stage PWM value change table. The input value determining section183′ then gives an instruction to rotate the fans (step S315).Specifically, the input value determining section 183′ instructs thepulse generator 15 b to input the pulse of the rear-stage PWM valuewhich has been determined at step S312 into the rear-stage fan 3 b.Owing to the above mentioned operation, the pulse of the rear-stag PWMvalue conforming to the revolution number of the front-stage fan 3 a isinput into the rear-stage fan 3 b and the revolution numbers of thefront-stage fan 3 a and the rear-stage fan 3 b come into coincidencewith each other in the predetermined tolerance.

As described above, in the embodiment 3, in the case that the differencein revolution number between the front-stage fan 3 a and the rear-stagefan 3 b is out of the predetermined tolerance, the revolution number ofthe rear-stage fan is changed such that the difference in revolutionnumbers between the fans is set in the predetermined tolerance. Owing tothe above mentioned operation, it may become possible to more set thedifference in revolution number between the front-stage fan 3 a and therear-stage fan 3 b in the predetermined tolerance.

Although several embodiments haven been described in detail withreference to the accompanying drawings, these embodiments are merelyexamples and the embodiments may be modified in other forms which arealtered and improved in a variety of ways on the basis of skills ofpersons in the art including the embodying aspects as described above.

For example, although in the above mentioned embodiments, the databasepreparing section 184 is used only in the case thatheating-element-temperature-based PWM value determination tables 71 a to71 b and the environmental-temperature-based PWM value determinationtables 72 a to 72 c are prepared, the revolution numbers of the fans 3 aand 3 b may be controlled using the database preparing section 184.

Specifically, first, the database preparing section 184 acquires thetemperatures of the heating elements or the environmental temperaturefrom the temperature information acquiring section 182. Then, thedatabase preparing section 184 calculates a front-stage PWM value and arear-stage PWM value of pulses to be input into the respective fans 3 aand 3 b in the case that an air flow rate needed for cooling the heatingelements 52 a and 52 b is obtained in a state in which a difference inrevolution number between the fans 3 a and 3 b is in a predeterminedtolerance on the basis of the acquired temperature(s). Then, thedatabase preparing section 184 notifies the input value determiningsection 183 (or the input value determining section 183′) of thecalculated front-stage PWM value and rear-stage PWM value.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the inventionand the concepts contributed by the inventor to furthering the art, andare to be construed as being without limitation to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although the embodiments of the presentinvention have been described in detail, it should be understood thatthe various changes, substitutions, and alterations could be made heretowithout departing from the spirit and scope of the invention.

1. A fan controlling apparatus for controlling a plurality of fans whichare tandemly arranged in ventilation direction of a chamber to control atemperature of a hot generating object placed in the chamber,comprising: a memory for storing data of the rotational speed each offans in relation to the temperature of the heat generating object; and acontroller for controlling the rotational speed of each of the fansrespectively in dependence on the temperature of the heat generatingobject in reference to the data stored in the memory.
 2. The fancontrolling apparatus according to claim 1, wherein the controllercontrols the rotational speed of each of the fans so that the differenceof an actual rotational speed of each of the fans lower thanpredetermined value.
 3. The fan controlling apparatus according to claim1, wherein the data that the memory stored are control parameters ofeach of the fans with respect to a plurality of the temperatures.
 4. Thefan controlling apparatus according to claim 3, wherein the controlparameters are respectively values of pulse width in accordance with thepulse width control of each fan, and the parameters are respectivelyparameters corresponding to pulse width inputs to each of the fans. 5.The fan controlling apparatus according to claim 1, wherein thecontroller controls the rotational speed of each of the fans so that thedifference of an actual rotational speed of each of the fans lower than10 percents.
 6. A fan controlling method for controlling a plurality offans which are tandemly arranged in ventilation direction of a chamberto control a temperature of a hot generating object placed in thechamber, comprising: detecting the temperature of a hot generatingobject; and controlling the rotational speed of each of the fansrespectively in dependence on the temperature detected in reference todata stored in the memory, the memory storing the data of the rotationalspeed each of fans in relation to the temperature of the heat generatingobject.
 7. The fan controlling method according to claim 6, wherein thecontrolling controls the rotational speed of each of the fans so thatthe difference of an actual rotational speed of each of the fans lowerthan predetermined value.
 8. The fan controlling method according toclaim 6, wherein the data that the memory stored are control parametersof each of the fans with respect to a plurality of the temperatures. 9.The fan controlling method according to claim 8, wherein the controlparameters are respectively values of pulse width in accordance with thepulse width control of each fan, and the parameters are respectivelyparameters corresponding to pulse width inputs to each of the fans. 10.The fan controlling method according to claim 6, wherein the controllingcontrols the rotational speed of each of the fans so that the differenceof an actual rotational speed of each of the fans lower than 10percents.
 11. A computer-readable recording medium storing a computerprogram controlling a plurality of fans which are tandemly arranged inventilation direction of a chamber to control a temperature of a hotgenerating object placed in the chamber, the program being designed tomake a computer perform the steps of: detecting the temperature of a hotgenerating object; and controlling the rotational speed of each of thefans respectively in dependence on the temperature detected in referenceto data stored in the memory, the memory storing the data of therotational speed each of fans in relation to the temperature of the heatgenerating object.